Project description:The loss of the tail is among the most notable anatomical changes to have occurred along the evolutionary lineage leading to humans and to the 'anthropomorphous apes'1-3, with a proposed role in contributing to human bipedalism4-6. Yet, the genetic mechanism that facilitated tail-loss evolution in hominoids remains unknown. Here we present evidence that an individual insertion of an Alu element in the genome of the hominoid ancestor may have contributed to tail-loss evolution. We demonstrate that this Alu element-inserted into an intron of the TBXT gene7-9-pairs with a neighbouring ancestral Alu element encoded in the reverse genomic orientation and leads to a hominoid-specific alternative splicing event. To study the effect of this splicing event, we generated multiple mouse models that express both full-length and exon-skipped isoforms of Tbxt, mimicking the expression pattern of its hominoid orthologue TBXT. Mice expressing both Tbxt isoforms exhibit a complete absence of the tail or a shortened tail depending on the relative abundance of Tbxt isoforms expressed at the embryonic tail bud. These results support the notion that the exon-skipped transcript is sufficient to induce a tail-loss phenotype. Moreover, mice expressing the exon-skipped Tbxt isoform develop neural tube defects, a condition that affects approximately 1 in 1,000 neonates in humans10. Thus, tail-loss evolution may have been associated with an adaptive cost of the potential for neural tube defects, which continue to affect human health today.
Project description:The loss of the tail is among the notable anatomical changes to have occurred along the evolutionary lineage leading to humans and to the “anthropomorphous apes”, with a hypothesized role in contributing to human bipedalism. Yet, the genetic mechanism that facilitated tail-loss evolution in hominoids remains unknown. Here, we present evidence that an individual insertion of an Alu element in the genome of the hominoid ancestor may have contributed to tail-loss evolution. We demonstrate that this Alu element – inserted into an intron of the TBXT gene – pairs with a neighboring ancestral Alu element encoded in the reverse genomic orientation and leads to a hominoid-specific alternative splicing event. To study the effect of this splicing event, we generated multiple mouse models that express both full-length and exon-skipped isoforms of mouse Tbxt, mimicking the expression pattern of its hominoid ortholog TBXT. We found that mice expressing both Tbxt isoforms can exhibit a complete absence of the tail or a shortened tail, depending on the relative abundance of Tbxt isoforms expressed at the embryonic tail bud, supporting the notion that the exon-skipped transcript is sufficient to induce a tail-loss phenotype. We further noted that mice expressing the exon-skipped Tbxt isoform may develop neural tube defects, a condition that affects ~1/1,000 neonates in human. Thus tail-loss evolution may have been associated with an adaptive cost of the potential for neural tube defects, which continue to affect human health today.
Project description:The loss of the tail is one of the main anatomical evolutionary changes to have occurred along the lineage leading to humans and to the “anthropomorphous apes”. This morphological evolution in the ancestral hominoids has long been considered to have accommodated a characteristic style of locomotion and contributed to the evolution of bipedalism in humans. Yet, the genetic mechanism that facilitated tail-loss evolution in hominoids remains unknown. Primate genome sequencing projects have made possible the inference of causal links between genotypic and phenotypic changes, and enabled the search for hominoid-specific genetic elements controlling tail development. Here, we present evidence that an individual Alu element insertion in the genome of the hominoid ancestor may have contributed to tail-loss evolution. We demonstrate that this Alu element – inserted into an intron of the TBXT gene (also called T or Brachyury ) – pairs with a neighboring ancestral Alu element encoded in the reverse genomic orientation and leads to a hominoid-specific alternative splicing event. To study the effect of this splicing event, we generated multiple mouse models that express both full length and exon-skipped isoforms of mouse Tbxt, mimicking expression pattern of its hominoid ortholog TBXT. We found that mice expressing both Tbxt isoforms can exhibit a complete absence of the tail or a shortened tail, depending on the relative abundance of Tbxt isoforms expressed at the embryonic tail bud, supporting the notion that the exon-skipped transcript is sufficient to induce a tail-loss phenotype. We further noted that mice expressing the exon-skipped Tbxt isoform – both in heterozygous and homozygous forms – may develop a neural tube defect condition, which affects ~1/1,000 human neonates. We speculate that tail loss evolution along the hominoid lineage may be associated with an adaptive cost of potential neural tube defects that may continue to affect human health today.
Project description:It has long been claimed that human emotional expressions, such as laughter, have evolved from nonhuman displays. The aim of the current study was to test this prediction by conducting acoustic and phylogenetic analyses based on the acoustics of tickle-induced vocalizations of orangutans, gorillas, chimpanzees, bonobos and humans. Results revealed both important similarities and differences among the various species' vocalizations, with the phylogenetic tree reconstructed based on these acoustic data matching the well-established genetic relationships of great apes and humans. These outcomes provide evidence of a common phylogenetic origin of tickle-induced vocalizations in these taxa, which can therefore be termed "laughter" across all five species. Results are consistent with the claims of phylogenetic continuity of emotional expressions. Together with observations made on the use of laughter in great apes and humans, findings of this study further indicate that there were two main periods of selection-driven evolutionary change in laughter within the Hominidae, to a smaller degree, among the great apes and, most distinctively, after the separation of hominins from the last common ancestor with chimpanzees and bonobos.